Paraffin oil or kerosene, used for lighting purposes, is a clear mobile
liquid, sometimes colourless, but usually more or less yellow and fluorescent
and of characteristic odour. Physical as well as chemical tests are made.
1. Physical Tests
1. Colour.—The colour of lamp oil may be used as a basis for commer-
cial contracts. Its intensity is determined by Stammer's colorimeter (Fig.
43), which consists of two vertical brass cylinders
blackened inside, one of them, closed at the bottom by
a glass, being charged with the liquid to be examined ;
in the other cylinder is inserted a standard glass
coloured with uranium oxide to a definite intensity,
and under both cylinders is a white reflecting "surface.
By means of two prisms, the two colours to be com-
pared are observed in the two halves of the circular
field of the eyepiece. The depth of the liquid may be
varied by vertical displacement of the system of prisms
along with a cylinder closed at the bottom by a glass
disc and dipping into the cylinder of liquid. When
uniformity of the field has been attained the depth of
the liquid giving a colour intensity equal to that of
the standard glass is read off on a scale.
The four grades of colour usually distinguished in
the trade, with the corresponding depths in Stammer's
colorimeter are :
In England and Russia, use is largely made of the Wilson colorimeter,1
which contains four standard coloured glasses corresponding with the
different commercial grades.
.2. Determination of the Specific Gravity.—As with crude petro-
leums, at 15°.
For determining the density of lamp oil for fiscal purposes, the Italian
Customs authorities use a thermo-aerometer graduated from 0750-0-840,
and tables of temperature corrections have been prepared.2
3. Fractional Distillation.—As with crude petroleum.
4. Flash Point.—Many forms of apparatus have been devised for this
purpose. The results obtained are purely conventional and vary from
1 Boverton Redwood: Petroleum, London, 1913.
2 Tables for the determination of the density and volume at 15°" of mineral oils,